In the field of microfabrication represented by the manufacture of integrated circuit devices, lithographic technology enabling microfabrication with 0.10 μm or less has been demanded in order to increase the degree of integration in recent years. However, microfabrication in a subquarter micron level is said to be very difficult using near ultraviolet rays such as i-lines which are generally used as radiation in a common lithography process. Therefore, in order to enable microfabrication with 0.10 μm or less, use of radiation with a shorter wavelength is being studied. As examples of such short wavelength radiations, bright line spectrum of a mercury lamp, deep ultraviolet rays represented by excimer lasers, X rays, electron beams, and the like can be given. A KrF excimer laser (wavelength: 248 nm) or an ArF excimer laser (wavelength: 193 nm) are given particular attention.
A number of resists (hereinafter referred to as “chemically-amplified resist”) utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a component (hereinafter referred to as “acid generator”) which generates an acid upon being exposed to radiation (hereinafter referred to as “exposure”) have been proposed as a resist suitable for being exposed to such an excimer laser. A chemically-amplified resist has been proposed which comprises a resin having t-butyl ester group of a carboxylic acid or t-butyl carbonate group of phenol and an acid generator. The t-butyl ester group or t-butyl carbonate group in the resin dissociates by the function of an acid generated upon exposure, whereby the resist has an acidic group such as a carboxyl group or a phenolic hydroxyl group. As a result, exposed areas on the resist film become readily soluble in an alkaline developer.
Formation of more minute patterns (a minute resist pattern with a line width of about 45 nm, for example) will he required for such a lithographic process in the future. Reducing the wavelength of a light source of a photolithography instrument and increasing the numerical aperture (NA) of a lens are thought to be means for foiming such a pattern with less than 45 nm, as described above. However, an expensive exposure machine is necessary for reducing the wavelength of a light source. In addition, increasing the numerical aperture (NA) of a lens involves a problem of decreasing the depth of focus even if resolution is increased due to a trade-off relationship between the resolution and the depth of focus.
Recently, a liquid immersion lithographic process has been reported as a lithographic technique enabling a solution for such a problem. In the liquid immersion lithographic process, a liquid refractive-index medium (liquid for liquid immersion lithography) such as pure water and a fluorine-containing inert liquid is caused to be present between a lens and a resist film on a substrate while having a specified thickness, at least on the surface of the resist film. In this method, when air or an inert gas such as nitrogen in a light-path is replaced by a liquid having a larger refractive index (n) such as pure water, the resolution can be increased without a decrease in depth of focus by using a light source with a given wavelength to the same degree as in the case in which a light source with a shorter wavelength is used, or the case in which a higher NA lens is used. Since a resist pattern having a higher resolution and excellent depth of focus can be formed at a low cost using the lens mounted on existing apparatuses by utilizing the liquid immersion lithography, the liquid immersion lithography has gotten a great deal of attention.
In the above-mentioned liquid immersion lithographic process, however, an acid generator and the like is eluted from the resist film since the resist film is brought into direct contact with the liquid for liquid immersion lithography such as water during exposure. When a large amount of the components is eluted, the lens may be damaged, a pattern having a prescribed shape may not be obtained, and a sufficient resolution may not be obtained.
Additionally, in the case where water is used as the liquid for liquid immersion lithography, water may not be sufficiently removed during high speed scanning exposure and watermarks may be left, if a receding contact angle between the resist film and water is small.
Resins described in Patent Document 1 and Patent Document 2, and additives described in Patent Document 3 have been proposed as a resin for using in a liquid immersion lithographic apparatus.
However, the receding contact angle between the resist and water is not necessarily sufficient in resists in which these resins and additives are used. A small receding contact angle tends to leave watermarks due to poor water removal during high speed scanning exposure. Moreover, the proposed resists do not necessarily sufficiently suppress elution of an acid generator and the like in water.
[Patent Document 1] WO 2004/068242
[Patent Document 2] JP-A 2005-173474
[Patent Document 3] JP-A 2006-48029